Inductively powered mobile sensor system

ABSTRACT

An inductively powered sensor system includes a primary conductive path  100  capable of being energised to provide an electromagnetic field in a defined space  1 . An inductive power pick-up  120  is associated with a sensor  124  and is capable of receiving power from the field to supply the sensor  124 . The system includes a first sensing means to sense the power available to the pick-up  120  and control means to increase or decrease the power available to the sensor dependant on the sensed power available. A method of inductively powering a sensor, an inductively powered sensor and an animal enclosure including one or more primary conductive path of an inductive power supply are also disclosed.

FIELD OF THE INVENTION

This invention relates to inductive supply of power to mobile sensors.The invention has particular application to a wireless power supply forbiosensors that are implanted in living creatures (including humans) andtransmit data representative of the physiological parameters to areceiver through a wireless link.

BACKGROUND

Physiological parameters in animals are measured using sensors which areplaced near, on or under the skin. Wires then carry the signal from thesensor to an external amplifier and display unit. This method has anumber of undesirable limitations, some of which include: theintroduction of movement artifacts; restraints of movement exacerbatingan unnatural environment; a potential source of infection, and;reliability problems with wires becoming tangled, breaking, or beingbitten.

Some systems presently exist for the wireless monitoring of animals,however these systems have power management problems. Typically, thewireless systems that are presently available require a battery to beprovided to power the sensor. This battery must be carried by theanimal. The battery is often bulky which can cause difficulties whenproviding the sensor unit within the animal. Also, there is an inabilityto remotely undertake long term recordings of physiological parametersbecause the batteries need to be removed so that they may be replaced orrecharged.

Wireless supply of power to biosensors has been attempted, but thesesystems either require a tightly controlled coupling between thebiosensor and power source, or can only supply sufficient power formonitoring slowly changing parameters, such as temperature. Controllingthe power transferred to the sensor can be difficult because the poweravailable varies depending on location and orientation of the sensorwith respect to the power source. Excess power is dissipated as heat inthe sensor. This is obviously highly undesirable causing discomfort orharm to the animal in which the sensor has been implanted, andexacerbating an unnatural environment for the animal.

Contactless power supplies that transfer power inductively have beenextensively developed. These have a primary conductive path (usually acable arranged on an elongate track) which is energised by a powersupply to produce an electromagnetic field about the primary path. Oneor more power pick-ups are provided closely adjacent to the path. Eachpick-up has a tuned circuit which receives energy from the field anduses this to supply a load. These power supply systems are typicallyadapted to supply power over a carefully controlled relatively short airgap of approximately 1 cm.

To power a biosensor, for example in an animal in a defined space suchas an enclosure or a cage, the power transfer system must deal withgreater physical separation and arbitrary orientation between theprimary conductive path and pick-up.

U.S. Pat. No. 6,345,203 discloses magnetic vector steering for poweringmultiple implant devices. It also refers to communication with animplanted device via the electromagnetic filed which energises theimplanted device. The energy status of an implanted device can bemonitored. However, this does not address problems with heatdissipation. Furthermore, although the implants are referred to as“arbitrarily oriented”, the system relies on a known configuration ofimplanted devices in relation to the primary coil. The implants aredisclosed as being provided in a fixed location with respect to theprimary field generating coils. Thus, the problems of variable distanceand random orientation of implants in relation to the primary coils arenot addressed.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvedinductively powered sensor apparatus and/or system.

Alternatively, it is an object of the invention to provide an improvedmethod for supplying power to a sensor.

Alternatively, it is an object of the invention to provide a method,apparatus or system for providing an inductively powered sensor whichwill at least provide the public with a useful choice.

In a first aspect the invention consists in an inductively poweredsensor system, the system including:

-   -   a primary conductive path capable of being energised to provide        an electromagnetic field in a defined space,    -   an inductive power pick-up associated with a sensor, the pick-up        being capable of receiving power from the field to supply the        sensor,    -   a first sensing means to sense the power available at the pickup        from the field,    -   control means to increase or decrease the power received at the        pick-up dependant on the sensed power available at the pick-up.

Preferably a second sensing means is provided to sense the immediatepower requirement of the sensor and wherein the control means toincrease or decrease the power available to the sensor so that the poweravailable to the sensor substantially matches the immediate powerrequired by the sensor.

Preferably the control means varies the field by altering the frequencyof the field to tune or de-tune the field toward or away from an optimalresonant frequency of the pick-up.

Alternatively the control means varies the field by increasing ordecreasing the current or voltage supplied to the primary conductivepath.

Alternatively the control means varies the field by varying a vector ofthe field.

Alternatively the control means varies the optimal resonant frequency ofthe pick-up.

Alternatively the control means varies the power flow using acombination of the techniques discussed above.

Preferably the first sensing means sense the power available to thepick-up by sensing a voltage provided by the pick-up.

Preferably the second sensing means sense the immediate powerrequirement of the sensor by sensing a current drawn by the sensor.

Preferably the first sensing means sense the power available to thepick-up by sensing a location of the sensor within the defined space.

Preferably the system includes a transmission means to transmit theimmediate power requirement of the sensor to the control means.

Preferably the system includes a transmission means to transmit thepower available to the pick-up to the control means.

Preferably the transmission means also transmit physiological datasensed by the sensor.

Preferably the sensor includes a charging means to charge an energystorage device from power supplied by the pick-up, so that power isavailable to the sensor when power is not supplied by the pick-up.

Preferably the control means provide the field only when the energystorage device requires charging.

Preferably the pick-up includes a plurality of pick-up coils oriented indifferent directions.

Preferably the sensor includes vector sensing means to sense theorientation of the pick-up relative to a vector of the field.

Preferably a plurality of primary conductive paths are provided to allowthe control means to vary the field vector.

Preferably the sensor includes vector sensing means to sense theorientation of the pick-up relative to a vector of the field and thecontrol means varies the field vector dependent on the sensedorientation.

Preferably the control means sweeps the frequency of the field to locatea resonant frequency or near resonant frequency of a pick-up.

Preferably a plurality of primary conductive paths are provided and aplurality of sensors are provided, each sensor having a separate pick-upassociated therewith, and the control means varies the field toselectively make power available to each sensor.

Preferably the sensor is a biosensor.

-   -   In a further aspect the invention consists in a method of        inductively powering a sensor provided in a defined space, the        method including:        -   generating an electromagnetic field in the defined space,        -   sensing the power available to a sensor provided in the            defined space, and        -   controlling the field to increase or decrease the power            available to the sensor dependant upon the sensed power            available.

Preferably the method includes sensing the power requirement of thesensor and controlling the field to increase or decrease the poweravailable to the sensor so that the power available to the sensorsubstantially matches the immediate power required by the sensor.

Preferably the step of varying the field includes the step of increasingor decreasing the frequency of the field.

Preferably the control means varies the field by increasing ordecreasing the current or voltage supplied to the primary conductivepath.

Preferably the control means varies the field by varying the fieldvector.

Preferably the sensor includes a charging means to charge an energystorage device from power supplied by the pick-up so that power isavailable to the sensor when power is not supplied by the pick-up, andthe method includes controlling the field to provide power only when theenergy storage device requires charging.

Preferably the method includes the step of sensing the orientation ofthe pick-up relative to a vector of the field.

Preferably the method includes the step of controlling the field vectordependent on the sensed orientation.

Preferably the method includes the step of sweeping the frequency of thefield to locate a resonant frequency or near resonant frequency of thepick-up.

Preferably a plurality of primary conductive paths are provided and aplurality of sensors are provided, each sensor having a separate pick-upassociated therewith, and the method includes varying the field toselectively make power available to each sensor.

Preferably the sensor is a biosensor.

In a further aspect the invention consists in an inductively poweredsensor including

first sensing means to sense the power available to the sensor from aninductive power pickup, and

transmission means to transmit sensed information to a remote controldevice for controlling the power available to the sensor.

Preferably the sensor includes second sensing means to sense theinstantaneous power requirement of the sensor for provision to thetransmission means.

Preferably the sensor includes vector sensing means to sense theorientation of the pick-up relative to a vector of a field supplyingpower to the pick-up and provide the sensed information to thetransmission means.

Preferably the sensor includes a charging means to charge an energystorage device from power supplied by the pick-up, so that power isavailable to the sensor when power is not supplied by the pick-up.

Preferably the pick-up includes a plurality of pick-up coils oriented indifferent directions.

Preferably the sensor is a biosensor.

Preferably the transmission means transmit physiological data sensed bythe biosensor.

In a further aspect the invention consists in an animal enclosure havinga perimeter defined by one or more walls, floor and/or ceiling andincluding one or more primary conductive path of an inductive powersupply in or about the or any part of the perimeter so that upon theprimary conductive path being energised an electromagnetic field isprovided within the enclosure.

Preferably the enclosure comprises a cage.

Preferably the enclosure comprises an animal rest area of a largeranimal enclosure.

Preferably the enclosure comprises an animal feed station of a largeranimal enclosure.

Preferably a plurality of primary conductive paths are provided and arearranged to provide electromagnetic fields having different fieldvectors.

Preferably the primary conductive path comprises a multi-turn coil.

Preferably the enclosure includes a power supply for energising orcontrolling energisation of the primary conductive path.

Preferably the enclosure includes a radio frequency receiver forreceiving information transmitted by a sensing device.

-   -   In a further aspect the invention consists in an inductively        powered sensor system, the system including:        -   a primary conductive path capable of being energised to            provide an electromagnetic field in a defined space,        -   an inductive power pick-up associated with a sensor, the            pick-up being capable of receiving power from the field to            supply the sensor,        -   a sensing means to sense the power requirement of the            sensor,        -   control means to vary the field to increase or decrease the            power available to the sensor dependant on the sensed power            requirement of the sensor.

According to a further aspect the invention consists of an inductivelypowered sensor system substantially as herein described with referenceto any one of the embodiments shown in the drawings.

According to a further aspect the invention consists of a method ofpowering a sensor substantially as herein described with reference toany one of the embodiments shown in the drawings.

According to a further aspect the invention consists of an inductivelypowered sensor substantially as herein described with reference to anyone of the embodiments shown in the drawings.

According to a further aspect the invention consists of an animalenclosure substantially as herein described with reference to any one ofthe embodiments shown in the drawings.

Further aspects of the invention, which should be considered in all itsnovel aspects, will become apparent to those skilled in the art uponreading the following description which provides at least one example ofa practical application of the invention.

BRIEF DESCRIPTION OF DRAWINGS

One or more embodiments of the invention will be described below by wayof example only and without intending to be limiting with reference tothe following drawings, in which;

FIG. 1 is a diagrammatic view of an enclosure such as a cage containingan animal,

FIG. 2 is a circuit diagram for a power pick-up circuit

FIG. 3 is a circuit diagram for a power supply

FIG. 4 is a diagrammatic perspective view of three pick-up coils

FIG. 5 is a circuit diagram showing pick-up circuit for use with thepick-up coils of FIG. 4

FIGS. 6 a-6 e show various configurations of conductors arranged aboutthe enclosure of FIG. 1 to provide a magnetic field within the enclosure

FIG. 7 a is a plot of available electrical power in a cross sectionthrough the enclosure of FIG. 6 c in the same plane as the primaryconductor

FIG. 7 b is a plot of pick-up voltage distribution measured in plan viewthrough the enclosure of FIG. 6 c, in the same plane as the primaryconductor

FIG. 8 is a diagram of a control circuit for controlling the fieldprovided in an enclosure such as the enclosure of FIG. 1

FIG. 9 is a plot of power against distance showing the power received bya pick-up in a quadrant of a space bordered by a primary conductor

FIG. 10 is a perspective view of an animal enclosure provided with afurther enclosure being a feed station

FIG. 11 is a perspective view of an animal enclosure provided with afurther enclosure being a rest area

FIG. 12 is a schematic diagram illustrating the components of aninductively powered biosensor.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, an enclosure in the form of an animal cage is showngenerally referenced 1 containing an animal such as a mouse 2. Althoughthe invention will be described with reference to a cage suitable forcontaining a small animal such as a mouse, those skilled in the art willappreciate that the invention is generally applicable to the wirelesssupply of power to a very wide range of animals (including humans orother living creatures) within a defined space. Furthermore, althoughthe invention is described below in relation to biosensors, thoseskilled in the art will realise that the invention is applicable toother sensors.

An electromagnetic field may be established in the space defined by theenclosure by providing an alternating current in a primary conductoradjacent to the cage 1. Electrical energy may be transferred from thefield to a tuned inductive pick-up circuit implanted in the animal 2.The pick-up circuit can thus provide the power supply required by abiosensor implanted in the animal.

We have found that a circuit such as that shown in FIG. 2 may be used inthe pick-up to provide a power supply to a biosensor B. The operation ofthis circuit has been described in our pending international applicationno. WO2004/105208 the disclosure of which is incorporated herein byreference. In brief, operation of this circuit is as follows. A pick-upcoil 10 has a voltage (represented by V_(S0)) induced therein when it isin the presence of an appropriate electromagnetic field. A tuningcapacitor 12 (C_(S)) has a value chosen to provide a desired resonantfrequency so as to optimise the transfer of energy from theelectromagnetic field to the pick-up. A rectifier circuit 22 rectifiesthe current from the resonant circuit and filters it through a DCinductor 24 (L_(S1)) and a filter capacitor 26 (C_(F)) to supply thedesired output voltage V_(D). A voltage and phase detection circuit 28and a gate control circuit 30 control the switches 18 and 20. Modules 28and 30 may alternatively be implemented in software.

Heat generation in an implanted sensor is highly undesirable. Thecircuit shown in FIG. 2 includes an optional controlled reactive element14. This element forms one example of a system capable of preventingheat generation when the power available from the tuned circuit of thepickup system exceeds the power requirements of the load. Element 14 maycomprise an inductor or capacitor 16 which is selectively switched intoor out of the resonant circuit of the pick-up by control of switches 18and 20 (S1 and S2). In this way, the resonant frequency of the pick-upcan be varied to allow the power received by the pick-up to varydependant upon the requirements of the load (i.e. the requirements ofbiosensor B) and the strength of the magnetic field flux experienced bythe pickup coil. The circuit shown and described with reference to FIG.2 effectively eliminates generation of unnecessary heat.

In order to generate a required electromagnetic field in the primaryconductor to supply the pick-ups which power the biosensors, a primarypower supply is required. We have found that an appropriate supply maybe one such as that shown in FIG. 3, the operation of which is describedin detail in our pending international patent application no.WO2004/105226 the disclosure of which is incorporated herein byreference. In brief, a DC supply 32 provides a current I_(D) to a DCinductor 34 and then to inductors 36 and 38 which split the supply.Switches 40 and 42 are switched on alternately to allow the supply to beswitched through a resonant circuit comprising a load 44 represented byvariable resistance R that has a corresponding inductance represented byinductor 46. A tuning capacitor 48 provides the desired resonantfrequency. However, a further reactive element which may comprise aninductor or capacitor (or combinations of these elements) 50 isprovided. This element provides a second example of how power flow canbe adjusted to match power availability at the pickup to biosensor loadrequirements to avoid generating heat within the biosensor assembly. Forease of illustration the reactive element 50 is shown as a simplevariable inductor or capacitor, but is implemented in practice usingsemiconductor switches between each terminal of a selected capacitanceor inductance and the terminals of tuning capacitor 48. The variablecapacitance or inductance is controlled by voltage and phase detectioncircuitry 52 and gate drive control circuitry 54 (which mayalternatively be implemented using software). In this way the resonanceof the resonant circuit can be varied to tune the electromagnetic fieldto the desired frequency.

The inductor 46 and the load R represent the primary conductor (and itsload) which is provided as a coil (either a partial turn, a single turnor most preferably multiple turns). The primary conductor is locatedabout or adjacent to the enclosure 1, and we have found that anelectromagnetic field of sufficient strength may be generated within thespace to allow the pick-up shown in FIG. 2 to provide a required powersupply for a biosensor. For example, the field may be generated at 200kHz, and the biosensor may require a DC voltage of approximately 3 voltsand a continuous current of approximately 10 milliamps. The relativelyhigh field frequency allows physically small components to be used.Also, the detuning control allows some variation in component values, sotolerances are not critical.

The pick-up circuit of FIG. 2 can be provided in relatively smallphysical form, for example an encased unit small enough to be implantedin relatively small animals such as mice, to allow continuous operationof a biosensor.

The pick-up coil can comprise a partial turn coil, or a single ormultiple turn coil and can be formed in a variety of different ways. Inone example, the coil may simply comprise a partial turn of conductivematerial provided on a printed circuit board. In another embodiment, thepick-up may comprise a multi-turn coil mounted on a circuit board, ormounted within a cut out space on a circuit board in order to keep spaceto a minimum. The coil may also include a material having magneticproperties, for example a ferrite core, to enhance field strength andthus power transfer capacity. In one embodiment the ferrite core mayprovide a battery housing (if a battery is provided) or facilitatelocation of the battery or a similar device such as a supercapacitor.

In another embodiment multiple pick-up coils may be provided. Turning toFIG. 4, a multiple coil pick-up arrangement is shown diagrammatically ona piece of circuit board 60. Pick-up coil 10 x is arranged in a verticaldirection as shown in FIG. 4. Pick-up coil 10 y is arranged in ahorizontal direction directed across the page as shown in FIG. 4, andpick-up coil 10 z is arranged in a horizontal direction arranged alongan axis which runs “in to or out of” the page as shown in FIG. 4.Therefore, the configuration shown provides coils which are mountedperpendicularly to each other so that they have axes corresponding to x,y and z axes of three dimensional space.

Turning to FIG. 5, a pick-up circuit which may be used with the coilsshown in FIG. 4 is illustrated. Referring to that figure, each of thepick-up coils has a tuning capacitance represented by capacitor 62. Afurther capacitor 66 can be controllably switched in parallel withcapacitor 62 by a control transistor 68. The output of the pick-upcircuit is rectified by Shottky Diode 70. The output from each of theShottky Diodes 70 is then provided to a control stage where it isinitially filtered by a filter capacitor 72 for provision to thebiosensor load B. A comparator 74 and associated resistive network(resistors 76 to 80) controls the natural resonant frequency of each ofthe pick-up coils by activating or deactivating transistor 68. Thisallows the power transferred to the pick-ups to be controlled to matchthe power requirements of the biosensor load B. A single controller isused to control three pick-ups at the same time, so the pick-up size andpower losses are smaller than using three separate circuits. Thecontroller may over tune or under tune the pick-up to control the powerflow.

Those skilled in the art to which the invention relates will see thatthe multiple pick-up coil arrangement described above (or even a singlepick-up coil arrangement) may be provided using a pick-up circuit thatdoes not include a variable reactive element i.e. a pick-up having afixed resonant frequency pick-up circuit may be used. Furthermore, coildirectional arrangements other than those described above may be used.

Turning to FIGS. 6 a to 6 e, various arrangements of the primaryconductor for providing an electromagnetic field within the enclosurespace are shown. The conductors shown in FIGS. 6 a to 6 e are discussedbelow with reference to a coil of conductive material. However, thoseskilled in the art will realise that a partial, single or full turn ofconductive material may be provided rather than multiple turns.Referring to FIG. 6 a, a coil 100 is shown provided on or within a wallof the enclosure, such as being located externally at the base of thecontainer. In FIG. 6 b multiple coils are provided. This allows fieldsto be provided in localised locations throughout the enclosure. Anotherarrangement shown in FIG. 6 c illustrates a coil mounted externally ofthe container horizontally about a mid section of the container. In FIG.6 d, the arrangement of FIG. 6 c can further include another coilmounted about the mid section of the container but in a vertical plane.In FIG. 6 e, coils are shown mounted about the periphery of the base ofthe container and about the ends of the container. Therefore, coils maybe located in a variety of different locations in or about any part ofthe one or more walls, floor and/or ceiling that define the perimeter ofthe enclosure. Primary coils may also be located at various locationsinside the enclosure. The available electrical power and voltagedistribution inside the enclosure and in the same plane as the coilshown in FIG. 6 c is shown in FIGS. 7 a and 7 b respectively.

The primary circuit, such as that shown in FIG. 3, may be controlled tocontrollably vary the field based on the instantaneous powerrequirements of each pick-up. These power requirements may be derivedfrom information retrieved from each pick-up, or based on otherinformation such as location of a pick-up, what the power requirementsof the pick-up should be at a given location or at a given time forexample, or a combination of these sources of information. Referring toFIG. 8, a feed back control system is diagrammatically illustrated.

Turning to FIG. 8, in this example a control system can be providedwhich has an input reference signal 110 corresponding to the powerrequired by the biosensor and associated circuitry that the pick-upsupplies. The pick-up 112 includes a transmitter (for example a devicewhich transmits RF signals representative of desired information) totransmit a signal representative of the current output voltage of thepick-up to a receiver 114. The received signals are compared with thereference to provide an error signal which is used by controller 115 tocontrol the power supply 116. The power supply may be controlled in anumber of different ways. For example, the magnitude of the voltage thatthe power supply provides to the primary conductor may be increased ordecreased to thereby change the field strength within the enclosure andthus vary the output of the pick-up. Therefore power received by thepick-up circuit can be fed back to the primary circuit controller tofacilitate adjustment of the electromagnetic field generated to maintainadequate power levels at the pick-up or to reduce the power level at thepick-up to prevent generation of unnecessary heat. Feed back iscurrently available through the use of a radio transceiver module (basedon an integrated circuit part number nRF24E1 from Nordic Semiconductor)with a data bandwidth of 1 Megabit per second and transmitting in the2.4 GHz frequency spectrum band. This transceiver module is primarilyused to digitise and transmit physiological data sensed by thebiosensor, but the pick-up power requirement data can also betransmitted using this module, for example by adding more digital datarepresenting power status to the packets being transmitted with digitalphysiological data. Capacitor buffering of the power supply to thebiosensors smoothes out short duration fluctuations such that adequatefeedback response time is easily achieved. The actual position ororientation of the pick-ups can also be detected to facilitate therequired power flow control.

Alternatively, a feed forward control system may be implemented. Forexample, the primary circuit controller can monitor the power beingdelivered to its own primary coil and use this to estimate the powerbeing drawn from the pick-up coil. When the pick-up coil is drawing lesspower than the level required by the biosensor, a primary controlalgorithm will attempt to increase power transfer by adjusting thegenerated field.

Independent pick-up systems (for example multiple animals within theenclosure) can be powered through the primary circuit controller using atime division multiplexing scheme to produce electromagnetic fieldsappropriate for each pick-up (for example at different frequencies orvectors) at different time slots.

The apparatus and systems described above may be implemented in avariety of different ways. As a first example, a single primaryconductor coil may be provided about the enclosure, such as for exampleis shown in FIG. 6 c. The coil is powered by a conventional powersupply, although a power supply such as that described with reference toFIG. 3 could be used if desired. The power supply is chosen so that itis sufficient to provide a field throughout the enclosure of sufficientstrength to power a pick-up. One or more animals is then provided in theenclosure, each animal having a biosensor device which is powered by apick-up such as the pick-up described with reference to FIG. 2. Thepick-up may also include an energy storage device such as are-chargeable battery or a supercapacitor to augment the wireless powersupply if required. Therefore, if the load cannot be met by the powersupply, the battery can assist until such time as the wireless supply issufficient at which time the battery may begin to be recharged by thewireless supply. For example, the electromagnetic field may be providedin a certain area of the enclosure that is visited frequently, such as afeeding station, and the battery may be recharged while the animal is inthat area. Alternatively, normal physiological data acquisition mayoccur under battery power in the animal's home cage, and the animalrelocated to the area containing the magnetic field for batteryrecharging. As another alternative, the biosensor may operate primarilyfrom the battery, so that the electromagnetic field is only generatedwhen the battery requires charging.

In another example, the primary power supply and primary conductor asdescribed immediately above are provided, but the pick-up deviceincludes the apparatus shown and described in FIGS. 4 and 5. This allowsthe field to be fully utilised independently of the orientation of thepick-up. The biosensor receives power continuously from the pick-up.

In another example, a pick-up which is tuned to a non-adjustableresonant frequency is used. Such a pick-up can be implemented by takingthe circuit of FIG. 2 and omitting the variable reactance 14 (and theassociated control modules). The power supply of the primary conductorcoil adjacent to the enclosure is adjusted to alter the power availableto the pick-up using one or more of the control strategies discussedbelow to allow the power requirements of the biosensor to be met. Theenclosure may be provided with a number of different primary conductorcoils, such as the enclosure shown in FIG. 6 b, 6 d or 6 e for example.For any independent pick-up with a single pick-up coil, best powertransfer is achieved when the magnetic field vector is orientedcorrectly with the pick-up coil. This may be achieved by energising aplurality of primary coils (usually by different amounts) at the sametime. This is equivalent to steering the orientation of the vector tobest match the pick-up coil orientation. Therefore, the vector may besteered dependent on pick-up location or orientation. When multiple,independent pick-ups are to be energised, a time division multiplexingscheme can be used in the primary controller to first generate amagnetic field vector steered to match the first pick-up, then nextgenerate a magnetic field vector steered to match the next pick-up inthe next time slot. Furthermore, if the feedback control discussed aboveis implemented, then the orientation of the field vector, magnitude ofthe field vector, or frequency of oscillation of the magnetic field canbe adjusted to control the power flow to the biosensor. As anotheralternative, multiple coils may be energised (for example using a timedivision multiplexing scheme) to provide a predictable or randomlychanging field within the cage to supply one or more pick-ups with asingle pick-up coil or a plurality of coils.

In yet another example, a number of different primary conductive pathsmay be provided, for example such as those shown in FIG. 6 b and thesemay be energised using one or more power supplies such that each coil isprovided at a different frequency and therefore directed to differentpick-ups so that selective pick-ups within animals may be selectivelypowered.

In another example, the configuration in 6 b may be used in such a waythat a position detecting system is provided. This may be achieved byenergisation of various coils to determine where the load exists forexample, and once the load has been located, energising the coil nearestto which the load is present so that a localised field in the requiredposition is provided. Position detection may also be achieved byinformation returned from the pick-up. Therefore, if the information onthe power requirement is compared with the field being generated, thenan estimate of the absolute position of the pick-up may be made for agiven pick-up orientation.

In a preferred embodiment of the invention, the pick-up that suppliespower to the biosensor is mounted on a printed circuit board with asingle pick-up coil. The pick-up coil in this embodiment comprises asingle turn (or near turn), or multiple turns of conductive materialsuch as copper track on or within the printed circuit board substrate.The board includes a transceiver module, and may include the biosensoritself, but is typically separately connected to the biosensor. In thisembodiment, a battery may also be provided, and the battery may bemounted on the printed circuit board. A primary conductor coil system isprovided about the cage or other defined space within which thebiosensor is to be operable. In FIG. 10 for example the primary coil 100is provided about an enclosure which defines a feeding station 102 whichin the embodiment shown comprises a hollow cylinder with an entry 104 atone end and a water bottle 106 or similar dispensing device providingfood or water through closed end 108. Similarly, as shown in FIG. 11, aprimary coil 100 may be provided about an enclosure defining a rest area110 comprising a compartment having an entry 112. FIGS. 10 and 11illustrate that the primary coil 100 can be provided in a selectedregion of a larger enclosure so that the field is confined to preventEMR problems. The pick-up does not include the de-tuning arrangementshown in FIG. 2, but the voltage supplied to the load (i.e thebiosensor) is detected, and provided to the transceiver module whichtransmits the information to a control unit associated with the powersupply for the primary coil. The control strategy illustrated withreference to FIG. 8 is then used to ensure that the pick-up is notsupplying power in excess of the needs of the biosensor and associatedcircuits, and therefore ensure that there is no unnecessary heat beingdissipated by the pick-up. The control strategy may also be used toensure that the biosensor is receiving sufficient power.

The field is controlled to limit the power supplied to the biosensor (orto increase it if necessary) by controlling one of three differentparameters, being:

-   -   a) magnetic field flux density;    -   b) magnetic field frequency of oscillation;    -   c) magnetic field vector (provided an appropriate coil        configuration is provided).

Each of these parameters is discussed briefly below.

The magnetic flux density may be controlled by controlling the magnitudeof the voltage applied to the primary coil. Therefore flux density canbe decreased by decreasing the voltage applied to the primary coil andtherefore reducing the power transferred to the pick-up.

The magnetic field frequency of oscillation is controlled by thefrequency of the current provided in the primary coil. By moving thefrequency of oscillation of the field toward or away from a naturalresonant frequency of the pick-up (i.e. an optimal frequency of thepick-up for power transfer), more or less power will be transferred tothe pick-up. It is desirable to have pick-ups with a high Q factor toimprove the quality of the resonant response in the pick-up and thusmaximize power transfer. A problem with using high Q circuits at apractical level is that component tolerances mean that it is difficultto provide pick-ups having the same resonant frequency. Also, componentvalues can vary over time. Variation of field frequency also allowspower to be provided to pick-ups having resonant circuits of a high Qfactor. This is because the primary supply can perform a frequency sweepfrom a low frequency to a higher frequency, or vice versa, untilfeedback shows that the pick-up has been energized, and from thefeedback provided by the biosensor the primary can lock onto a resonant,or near resonant, frequency of the pick-up and control the poweravailable to it. Variation of field frequency also allows control ofmultiple pick-ups by providing pick-ups with distinct different resonantfrequencies so that the field selectively makes power available to eachpick-up.

Magnetic field vector orientation can be controlled if there is morethan one primary coil by controlling the relative flux density generatedby each coil to provide a resultant field vector orientation. In apreferred embodiment the vector has six degrees of freedom tocharacterize (using location, magnitude and orientation) the magneticfield at any instant in time.

In this preferred embodiment the primary coil is provided about only aselected portion of the enclosure. Therefore, a battery may be used toprovide power to the sensor when the pick-up is out of range of theelectromagnetic field. When the pick-up is within range of theelectromagnetic field, the flow of power to the pick-up is controlled tomeet biosensor needs and battery charging needs. When the battery isfully charged, the power flow is controlled to a reduced level which issufficient to power the biosensor only. This strategy ensures that noexcess energy is dissipated as heat.

A diagram of the functional components of the biosensor unit of thisembodiment is shown in FIG. 12 where the pick-up system 120 suppliespower to a power flow controller 122 which controls the supply of powerto the biosensor 124 itself, a battery 126 (if provided) and thecommunications module 128. Although the pick-up system is shown ashaving a single rectifying diode, a full bridge rectifier may beprovided to increase power extraction from the pick-up resonant circuit.The power flow controller includes a sense resistor 130 which senses anindication of the power required by the biosensor (based on currentdrawn) and the communications module (which are supplied via voltageregulator 132). The indication of power required is provided to thecommunications module 128 along with the power required by the batterycharger 134 which is sensed via sense resistor 136, which again allowsan indication of current to be obtained. The communications moduleincludes a microprocessor operable to provide an indication of totalpower demand and provide that information to a transceiver (not shown inthis figure) which is part of the communications module. Line 140 sensesthe output voltage of the pick-up system so it can be used to provide anindication of available power to the pick-up. This information isprovided to the communications module for transmission by thetransceiver. Switch 142 is operable by the power flow controller toallow the battery to be charged, or connected to supply power to theunit via switch 144. The biosensor unit as a whole, as shown in FIG. 12may be provided as a single unit or one or more components may beprovided separately.

Also, there is the option of providing the pick-up with additionalmagnetic field coils in different orientations (as discussed withreference to FIG. 4), and it is also possible to select one of the coils10 x, 10 y or 10 z as the coil from which power is derived, and use theother two coils to provide feedback on the orientation of the pick-uprelative to the field. Coils not used for deriving power may bespecially designed for field detection. This information may be used toassist determination of the location of the pick-up, or to select thefield vector required for providing the desired power flow to thepick-up.

Implementation of the control strategy described above is now discussedwith reference to FIG. 9 and Table 1. FIG. 9 shows available power to apick-up device located on an enclosure base within a total area size of500 mm by 400 mm. The primary coil comprises of three turns enclosingthe base area and is located 50 mm above the enclosure base similar tothe concept shown in FIG. 6 c. The power level is normalized at the coilcentre, which is located at point x=0, y=0 where the power levelreceived was equal to the power need of a biosensor with a steady powerneed of 13 mW. The field is symmetrical in both x and y directions, soonly one quarter of the area is shown in FIG. 9. The power available tothe pick-up increases as the pick-up moves from the coil centre towardthe coil perimeter. There is a decrease in power available at x=250 mmcaused by close proximity of the biosensor to the primary coil andchanges in direction of the magnetic flux vector compared to the centerpoint. The pick-up used consists of a single coil formed using tracks ona printed circuit board of dimension 20 mm by 40 mm. The pick-up, andthe energisation of the primary coil are set to deliver 13 mW of powerat x=0, y=0 to match the power requirement of the biosensor. Thoseskilled in the art will appreciate that the power supplied to thebiosensor system in excess of 13 mW is power that will be dissipated asheat within the pick-up unless the power level of the pick-up iscontrolled so that the power supplied to the pick-up is reduced as thepick-up moves away from point x=0, y=0 toward the coil at the perimeter.

Referring now to Table 1, the first pair of columns define the locationof the pick-up and the remaining three columns show the frequency,voltage or vector orientation required to supply the pick-up with powerto match the biosensor requirements at the defined location. Therefore,for example, if the pick-up is located at point x=0, y=0, then thefrequency of the field is 200 kHz to supply the required 13 mW, thevoltage applied to the primary 60.4 V, and the angle of the primarymagnetic field vector with respect to the normal of the pick-up coil is0°. The reference (dno) refers to “data not obtained”.

TABLE 1 Location Location Frequency Voltage Control Vector Control x(mm) y (mm) (KHz) (Volts DC) (degrees) 0 0 200 60.4 0 100 0 171 57.127.5 200 0 153 48.4 45 0 100 160 51.6 35 100 100 dno 49.4 34 200 100 dno44 dno

If the location of the pick-up is changed to x=100 mm, y=Omm, then withthe voltage control being 60.4 V and the vector control being 0°, thenthe frequency of 171 kHz will reduce the power supplied to the pick-upback to the normalized level i.e back to the 13 mW. Similarly, if atlocation x=100 mm, y=0 mm, the frequency may be maintained at 200 kHzand the voltage in the primary coil reduced to 57.1 V while retainingthe vector control 0° to reduce the power supply to the pick-up to thenormalized level. Again, at X=100 mm, Y=0 mm, the frequency may bemaintained at 200 kHz, and the voltage on a primary coil maintained at60.4 V, but if the vector can be changed to 27.5° relative to the normalof the pick-up, then the power supplied to the pick-up will becontrolled to the required level.

Those skilled in the art will realize that control of theelectromagnetic field as discussed above means that power flow to thepick-up can be effectively regulated even when the field is disrupted byaddition of objects into the enclosure. For example the addition of ametal object into the enclosure will shift resonant frequencies, but thefeedback discussed above will allow the frequency of the field to beadjusted to compensate. Therefore, the invention is robust toenvironmental changes independent of the biosensor configuration and/orthe primary configuration.

Whilst the invention has been described with particular reference tobiosensors, it will be appreciated that the system and sensors of theinvention, which enable the control of power flow to sensors poweredinductively, may equally have application outside the field of biology.For example, in other circumstances where there are arbitrary andvariable relationships between the sensor(s) and the primary powersupply and where it is necessary to avoid heat generation in thesensors, such as in small or miniaturised industrial sensors.

Those skilled in the art will realize that the sensor may sense multipleparameters and may also be associated with an actuator. Examples ofactuator function include mechanical output (e.g pumps and releasemechanisms), ultrasonic transducers and electrical stimulation. Withsuch sensor/actuator systems power may be supplied through the sameprimary induction power system.

The invention advantageously allows frequency, voltage and vectoring ofthe field to be varied on the primary side and detuning to be used onthe pick-up side to allow effective control of the power available to,or supplied by, the pick-up. Those skilled in the art will appreciatethat these control parameters may be used in any desired combination.For example, primary frequency tuning may be used to find the resonantfrequency of the pick-up, after which primary voltage variation (orpick-up detuning) may be used to match power flow to immediate powerneed.

It should be noted that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications may be madewithout departing from the spirit and scope of the present invention andwithout diminishing its attendant advantages. It is, therefore, intendedthat such changes and modifications be included within the presentinvention.

Throughout this document the word “comprise” and variations such as“comprises” and comprising” is intended to be interpreted in aninclusive sense.

1-52. (canceled)
 53. An inductive power transfer system, the systemcomprising: a primary conductive path capable of being energized toprovide an electromagnetic field in a volume; an inductive power pick-upassociated with a device, the pick-up being capable of receiving powerfrom the field to supply the device when located in the volume; asensing circuit operable to sense power available to the pick-up; and acontroller operable to control the magnetic flux density of the fieldand the frequency of oscillation of the field dependent on the sensedpower available to the pick-up.
 54. A system according to claim 53,wherein the primary conductive path comprises at least one primary coiland the inductive power pick-up comprises at least one pick-up coil. 55.A system according to claim 54, wherein the controller is operable tocontrol the frequency of oscillation of the field by controlling thefrequency of the current in the at least one primary coil.
 56. A systemaccording to claim 54, wherein the controller is operable to control themagnetic flux density of the field by controlling the magnitude of thevoltage applied to the at least one primary coil.
 57. A system accordingto claim 56, wherein the primary conductive path comprises a pluralityof primary coils.
 58. A system according to claim 57, wherein thecontroller is operable to further control the vector of the field withinthe volume by controlling the relative magnetic flux density in at leasttwo of the primary coils.
 59. A system according to claim 54, whereinthe sensor comprises a vector sensing unit operable to sense anorientation of the at least one pick-up coil relative to the vector ofthe field.
 60. A system according to claim 53, wherein the pick-upcomprises a communications module operable to communicate the sensedpower available to the pick-up to the controller.
 61. A system accordingto claim 60, wherein the communications module is operable tocommunicate the immediate power requirement of the device to thecontroller.
 62. A method of inductively powering a device, the methodcomprising the steps of: generating an electromagnetic field in a volumeby energizing a primary conductive path; sensing power available to aninductive power pick-up located in the volume, using a sensing circuitassociated with the pick-up, the pick-up being associated with thedevice and being capable of receiving power from the field to supply thedevice; and controlling the field, using a controller associated withthe primary conductive path, to control the magnetic flux density of thefield and the frequency of oscillation of the field dependent on thesensed power available to the pick-up.
 63. A method according to claim62, wherein the primary conductive path comprises at least one primarycoil and the inductive power pick-up comprises at least one pick-upcoil, the controlling step comprising controlling the frequency ofoscillation of the field by controlling the frequency of the current inthe at least one primary coil.
 64. A method according to claim 62,wherein the primary conductive path comprises at least one primary coiland the inductive power pick-up comprises at least one pick-up coil, thecontrolling step comprising controlling the magnetic flux density of thefield by controlling the magnitude of the voltage applied to the atleast one primary coil.
 65. A method according to claim 64, wherein theprimary conductive path comprises a plurality of primary coils, thecontrolling step further comprising controlling the vector of the fieldwithin the volume by controlling the relative magnetic flux density inat least two of the primary coils.
 66. A method according to claim 65,further comprising the step of sensing, using a vector sensing circuit,an orientation of the at least one pick-up coil relative to the vectorof the field.
 67. A method according to claim 66, wherein thecontrolling step comprises controlling the field vector dependent on thesensed orientation.
 68. A method according to claim 62, furthercomprising the step of communicating the sensed power available to thepick-up to the controller.
 69. A method according to claim 68, whereinthe communicating step comprises communicating the immediate powerrequirement of the device to the controller.